"Judge Paul Kelly, an appointee of former president George H.W. Bush, was the most skeptical of same-sex marriage rights. Judge Carlos Lucero, appointed by Bill Clinton, appeared strongly in favor.

"That left George W. Bush's judge, Jerome Holmes, in the middle. He came out forcefully, wondering why bans on same-sex marriage are any more legitimate than earlier bans on interracial marriage, which were struck down by the Supreme Court. But he also expressed some support for Utah."

As The Associated Press notes, "Eight federal judges have, to varying degrees, agreed since the Supreme Court ruling, striking down a series of state gay marriage bans, or bans on recognizing same-sex marriages from other states."

Judge Lucerno said: "The law does not allow the type of discriminatory behavior that is at issue in these type of cases." But Kelly, questioning attorney Peggy Tomsic, who represents three gay couples, said her position simply ignored the will of the people of the state of Utah who approved the ban.

Tomsic argued that "any state law that bars gays from something as fundamentally important as marriage should be voided," The Associated Press says.

Colorado Public Radio's Megan Verlee, who was in the Denver courtroom, said both sides cited United States v. Windsor, the Supreme Court case issued last June.

Tomsic, the attorney for the three couples, "found language in Windsor that marriage is a fundamental right, protected by the U.S. constitution above and beyond any laws that states might pass," Verlee says.

"But on the other side, the attorney for the state of Utah argued that Windsor actually supports a federalist approach to marriage, where the states have the overriding right to set their marriage laws," she says.

Several other states — Texas, Michigan and Oklahoma among them — have also seen their marriage bans overturned in federal court, but the Utah case is the furthest along so far.

As a result, the U.S. Supreme Court is "incredibly likely" to rule definitively on gay marriage, possibly as soon as the next session, Verlee says.

Update at 2:50 p.m. ET 4/11:

As NPR's Howard Berkes points out, the 10th Circuit judges will hear oral arguments in the Oklahoma case next week and consider the Utah and Oklahoma cases together.